Plasma etch reactor and method

ABSTRACT

A plasma etch reactor  20  includes a upper electrode  24 , a lower electrode  24 , a peripheral ring electrode  26  disposed therebetween. The upper electrode  24  is grounded, the peripheral electrode  26  is powered by a high frequency AC power supply, while the lower electrode  28  is powered by a low frequency AC power supply, as well as a DC power supply. The reactor chamber  22  is configured with a solid source  50  of gaseous species and a protruding baffle  40 . A nozzle  36  provides a jet stream of process gases in order to ensure uniformity of the process gases at the surface of a semiconductor wafer  48 . The configuration of the plasma etch reactor  20  enhances the range of densities for the plasma in the reactor  20 , which range can be selected by adjusting more of the power supplies  30, 32.

This application is a divisional of Ser. No. 08/675,559, filed Jul. 3,1996, now U.S. Pat. No. 6,500,314.

FIELD OF THE INVENTION

The present invention relates to an improved plasma etch reactorapparatus and method.

BACKGROUND OF THE INVENTION

There are a number of prior art devices and methods used for plasmaetching of semiconductor wafers. One successful such apparatus andmethod is disclosed and depicted in U.S. Pat. No. 4,464,223, for which aReexamination Certificate was issued on Apr. 9, 1991. This plasma etchreactor depicts a reactor chamber which is bounded by three electrodes.An upper electrode is grounded, while a lower electrode is provided witha low frequency power supply along with a DC power supply. The lowerelectrode is also the chuck which holds the semiconductor wafer inposition. Another electrode is located between the upper and lowerelectrodes and is positioned about the periphery of the reactor chamberin substantially cylindrical in shape. This electrode is provided with ahigh radio frequency power supply. In this arrangement, the high and lowfrequency power supplies are used to optimize (1) the disassociation ofthe process gases, and (2) the ion energy of the plasma generatedreactant species.

While the above device has been very successful in operation, it hasbeen found that more precise control of the plasma within the reactorchamber would be beneficial to the operation of a plasma etch reactor.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to improving upon theoperation of prior plasma etch reactors.

It is an object of the present invention to provide a plasma etchreactor which has an increased range of plasma density in order toaffect and control the etching processes carried out in the reactorchamber. By way of example only, such enhanced plasma density range canfavorably affect the selectivity and the profile control of the etchingprocess.

It is a further object of the invention to provide a solid source whichcan be eroded to produce gaseous species that are advantageous to theetching process. It is also an object to controllably erode the solidsource so that there is an appropriate mixture of the eroded gaseousspecies and injected process gases.

It is a further object of the invention to provide a unique nozzlearrangement which allows jets of process gas to reach the surface of asemiconductor wafer in order to create a uniform distribution of processgases at the surface.

It is yet a further object of the invention to provide a protrudinginsulator or baffle in order to further confine the reactor chamber andensure that there is a uniform distribution of process gases and/or auniform distribution of process gases mixed with the gaseous speciesfrom a solid source.

It is yet another object of the invention to provide an enhancedmagnetic field in order to control the plasma created and the amount ofgaseous species which are generated from the solid source.

It is a further object of the invention to define the dimensions of thereactor chamber in order to ensure that there is a uniform distributionof fresh process gases at the surface of the semiconductor wafer.

It is yet a further object of the present invention to provide one ormore power sources association with one or more of the above featuresand objects in order to be able to select the desired plasma dens withinthe enhanced range of possible plasma densities by adjusting the powerprovided to electrodes of the reactor chamber.

Finally, it is still another object of the present invention to providea reactor chamber which has an increased range of plasma densities dueto a combination of any one or all of the above objects and features.

Additional features, objects, and aspects of the invention are evidentfrom the below description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a side cross-sectional view of an embodiment of the plasmaetch reactor of the invention.

FIG. 2 is a view similar to FIG. 1 with the addition of an enhancedprocess gas inlet nozzle.

FIGS. 3a and 3 b depict end and side cross-sectional views of apreferred embodiment of a nozzle of the invention.

FIGS. 4a, 4 b, 4 c, and 4 d depict isometric, side cross-sectional,enlarged partial side cross-sectional, and end views of anotherpreferred embodiment of a nozzle of the invention.

FIGS. 5a, 5 b, and 5 c depict side cross-sectional, enlarged partialcross-sectional, and end views of yet another preferred embodiment of anozzle of the invention.

FIGS. 6a, 6 b, and 6 c depict side cross-sectional, enlarged partialcross-sectional, and end views of still a further embodiment of a nozzleof the invention.

FIG. 7 depicts a perspective view of the arrangement of the magnetsassociated with a peripheral electrode of an embodiment of theinvention.

FIG. 8 depicts a perspective view of the arrangement of the magnetsassociated with the upper electrode of an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the figures and in particular to FIG. 1, a sidecross-sectional view of an embodiment of the plasma etch reactor 20 ofthe invention is depicted. This reactor 20 enhances and improves uponthe reactor depicted and described in U.S. Pat. No. 4,464,223, whichpatent is incorporated herein by reference.

Reactor 20 includes a reactor chamber 22 which is bounded by a groundedupward electrode 24, a side peripheral electrode 26, and a bottomelectrode 28. In a preferred embodiment, the side peripheral electrode26 is connected to a power supply 30 which provides power to the sideperipheral electrode 26 preferably at 13.56 MHz at a power level ofpreferably 1,100 watts. It is to be understood that this is a highfrequency power supply (preferably in the radio frequency range) andthat the frequency preferably can range from 2 MHz to 950 MHz. The powercan also preferably be supplied in the range of 200 watts to 3,000 wattswith a voltage of between 100 volts to 5,000 volts.

A second power supply 32 is connected to the bottom electrode 28. Thesecond power supply 32 is preferably operated at 450 KHz with the powerbeing preferably supplied at 30 watts, and at a voltage of 200 volts.This is the low frequency power supply. It is to be understood that thispower supply (preferably in the radio frequency range) can be operatedin the range of 10 KHz to 1 MHz with a power range of 2 watts to 1,000watts, and a voltage range of 5 volts to 3,000 volts. Also connected tothe bottom electrode 28 is a DC power supply 34. The high-frequencypower applied to the side electrode 26 controls ion flux, whilelow-frequency power applied to the bottom electrode 28 independentlycontrols ion energy.

It is the control of the power supplies and principally the highfrequency power supply which advantageously controls the density of etchplasma in order to provide superior etch characteristics. Further, it isthe design of reactor 20 which provides the enhanced plasma densityrange from which the optimal plasma density can be selected by thecontrol of the power supply.

Associated with the grounded upward electrode 24 is a central nozzle 36which directs a jet of process gas into the reactor chamber 22 directedat the semiconductor wafer 48. As will be discussed below in greaterdetail, the jets of process gas from the nozzle 36 are able toeffectively reach the surface of the semiconductor wafer 48 and providea fresh, uniform distribution of process gas over the entire surface ofthe semiconductor wafer 48.

Immediately above the grounded upper electrode 24 and the nozzle 36 isan exhaust stack 38, which is used to exhaust spent gas species from thereactor chamber 22. It is to be understood that a pump (not shown) issecured to the exhaust stack 38 in order to evacuate the gas speciesfrom the reactor chamber 22.

As can be seen in FIG. 1, immediately below the upper electrode 24 andnozzle 36 is a protruding, peripheral baffle 40. Baffle 40 is comprisedof insulating material, and as will be discussed below, protrudes intothe exhaust path 42 between the nozzle 36 and the housing 44 of theplasma etch reactor 20. Protruding baffle 40 ensures that there is agood-mixture of the various gas species from the nozzle 36 and the solidsource 50 in the reactor chamber 22.

Immediately below the protruding baffle 40 and in this embodimentincorporated into the side peripheral electrode 26 is a magnet orplurality of magnets 46. Also preferably incorporated in upper electrode24 is a magnet or plurality of magnets 47. As will be discussed below,either one or both of these magnets 46 and 47 define a magneticconfinement chamber about and coincident with the reactor chamber 22.This magnetic confinement chamber ensure that the charged ion species inthe reactor chamber do not leak therefrom, and that the charge ionspecies are concentrated about the semiconductor wafer 48. This magneticconfinement chamber inhibits the charged ion species from collecting onthe walls of the reactor chamber 22.

Covering the side peripheral electrode 26 and the magnets 46 is a sideperipheral solid source 50. This solid source 50 provides for aninnovative source of a gaseous species which can be sputtered throughthe bombardment of, for example, radio frequency excited ions whichknock or erode atoms of the gas species from the solid source 50 intothe reaction chamber 22. The erosion of gaseous species from the surfaceof the solid source can be affected by pulsing one or both of the aboveAC power supplies. As a further advantage, as portions of the surfacesof the solid source erode, no particles can be formed on the erodingsurface by the combination of gaseous species. Thus, contamination fromsuch particles formed on eroding portions of the solid surface areeliminated. Variations of the solid source 50 are discussed hereinbelow.

Immediately below the solid source 50 is the wafer chuck 52 whichpositions the semiconductor wafer 48 relative to the reactor chamber 22.Wafer clamp 53 holds the wafer 48 on the wafer chuck 52. In thisembodiment, the wafer chuck 52 as well as the bottom electrode 28 can bemoved vertically downward in order to insert and remove the wafer 48.

In this embodiment, if desired, the side peripheral electrode 26 and themagnets 46 can be cooled using a cooling water manifold 54. It isfurther to be understood that the solid source 50 can be heated ifdesired using a hot water manifold 56. Other methods of heating thesolid source 50, and particularly the front exposed surface thereof,include resistive and inductive heating, and radiant heat provided bylamps and other sources of photons.

The protruding baffle 40 as well as the configuration of the magnets andthe process gas jets from the nozzle, and the gas species eroded fromthe solid source, provide for a high density plasma adjacent to thesurface of the semiconductor wafer. This configuration greatly increasesthe range of densities that can be achieved within the reactor chamber22. The exact density required can be selected from the greater range ofdensities by controlling the power provided to the peripheral electrode26 by the power source 30. The power source can be turned down if thereis a desire to reduce the erosion rate of gas species from the solidsource, and to reduce the density of the plasma. Alternatively, thepower source may be turned up in order to increase the density of theplasma in the reactor chamber 22.

By way of example only, if a polysilicon layer is being etched, thepower provided by high frequency power source 30 would be turned down asa less dense plasma and a lower erosion rate is required from the solidsource 50. Alternatively, if a silicide is being etched, the power wouldbe turned up as a denser plasma and high erosion rate would be desiredfrom the solid source. Further, the lower frequency power source canalso be adjusted to affect the results of the etching process in theabove invention.

The above range of operation is not possible with prior devices. It isto be understood that one or more of the above features can be used toenlarge the plasma density range and thus improve the etch process andfall within the spirit and scope of the invention.

An alternative embodiment of the reactor 20 is shown in FIG. 2. Similarcomponents are numbered with similar numbers as discussed hereinabove.In FIG. 2, the nozzle 36 has been modified in order to improve theuniformity of the mixture of the gaseous species in reactor chamber 22.As can be seen in FIG. 2, the nozzle 36 includes a manifold 70 which canchannel the process gases in a number of directions. From manifold 70there are horizontal ports 72, 74 which direct jets of the process gaseshorizontally and parallel to the upper electrode 24. Port 76 directsjets of the gas vertically downward directly onto the wafer 48. Ports 78and 80 channel jets of the process gases in a direction skewed to thehorizontal, and principally toward the periphery of the wafer 48 inorder to assure a uniform distribution of process gases and/or a goodmixture of the gas species sputtered or otherwise eroded from the solidsource 50 and the jets of process gases. In this embodiment, it is alsothe combination of the ports of the manifold 70 and the protrudingbaffle 40 which ensures that a good mixture of (1) the gas speciessputtered or eroded from the solid source 50, and (2) the process gasesfrom the ports of the nozzle 36, are presented to the surface of thesemiconductor wafer 48.

In this alternative embodiment, if desired, a second low frequency powersupply 31 can be communicated with the peripheral electrode 26. Thispower supply would preferably have a frequency of 450 KHz. This powersupply would be in all aspects similar to power supply 32. The highfrequency power supply 30 would control the plasma density while the lowfrequency power supply 31 would control the erosion rate of gaseousspecies from the solid source. This would be an alternative to havingthe high frequency power supply control both the density of the plasmaand the rate of erosion in the solid source.

Etching in prior art devices is usually performed in the 300 to 500millitorr range, which range is one to two orders of magnitude higherthan the low pressures contemplated by the reactor of the presentinvention. For etching of submicron features required bystate-of-the-art semiconductor devices, low pressure operations aredesirable. However, at low pressures, it is more difficult to maintain ahigh density plasma.

For the embodiments of FIGS. 1 and 2, the present invention contemplatesa magnetic field which contains the plasma at a low pressure (3-5millitorrs), with a high plasma density (10¹¹cm³ at the wafer), and withlow ion energy (less than 15 to 30 electron volts). Generally, lowpressure operation would be at about 150 millitorr or about 100millitorr or less and preferably about 20 millitorr or about 10millitorr or less. For submicron (sub 0.5 microns) devices, the plasmasource must operate at a low pressure with a high density of activatedgases at the wafer and a low ion energy in order to deliver superioretching results. A low pressure plasma improves the overall quality ofthe etch by minimizing the undercutting of the wafer features as well asthe effect of microloading (etching concentrated features more rapidlythan less concentrated features), both of which can adversely affectoverall yield. Low pressure, however, requires a high density plasma atthe wafer to increase the number of plasma particles reacting with afilm on the semiconductor wafer being etched in order to maintain a fastetch rate. A fast etch rate is one factor leading to a higher averagethroughput. Further, low ion energy leads to improved etch selectivityand minimizes wafer damage. -Both of which improve overall yield. It iscontemplated that the present embodiments can operate at about 150millitorr or less.

The reactor 20 of the present invention can be used to etch a variety ofdifferent substrates or films which require different etch chemistry orrecipe. Generally, this chemistry includes two or more of the followinggases: halogen gases, halogen containing gases, noble gases, anddiatomic gases.

Variations of the above features describe above will now be explained ingreater detail.

Solid Source:

It has been determined that the gaseous species eroded or sputtered fromthe solid source 50 or the lack of species eroded or sputtered therefromcan have a profound effect on the success of the etching process carriedout in the plasma etch reactor 20. By way of example only, the solidsource 50 can be comprised of a dielectric material such as for examplesilicon dioxide (SiO₂) or quartz which upon bombardment by radiofrequency excited ions provide gaseous ions of silicon and oxygen fromthe solid source into the reaction chamber. Another type of dielectricsolid source can include a ceramic such as alumina (AL₂O₃). This ceramichas a low sputtering or erosion rate when impacted by excited gaseousions and is useful for situations where no additional contribution froma solid source is required or desired. Particularly, with respect toalumina, with a power supply under approximately 600 volts peak to peak,little or no sputtering is observed. Over that threshold, there issputtering from an alumina solid source.

Generally, the solid source can be comprised of a semiconductormaterial, a dielectric material, or a conductor. In fact, the solidsource could be embodied in the materials which comprise the electrode,and those materials can be eroded to provide appropriate gas species forthe plasma in the reactor chamber. Appropriate dielectric materials alsoinclude silicon nitride (Si₃N₄), in addition to other metal oxidesbesides alumina (Al₂O₃). Semiconductor materials can include siliconcarbide (SiC). Further, conductors can include graphites and aluminum.

The surface temperature of the solid source 50 is preferably above 80°C. in order to provide for adequate sputtering. At this temperature andwith the appropriate energized ions eroding the surface of these solidsource, the solid source does not become a cold sink for the formationof particles, as discussed herein, from gaseous species, which particlescan break away and contaminate the reaction chamber 22.

As discussed above, the rate of erosion or sputtering of the gaseousspecies from the solid source 50 can be controlled by the high frequencypower supply 30. By increasing the power supply 30, higher energy ionscan be used to bombard the solid source 50 in order to increase the rateof erosion of gaseous species from the solid source for purposes of theetching process. By way of example, should a solid source of silicondioxide be used, increased bombardment would enhance anisotropic etchingas the gaseous species sputter from the silicon dioxide would passivatevertical surfaces on the semiconductor wafer so that such surface wouldnot be undercut by the gaseous etchant species.

Further erosion of gaseous species from the solid source 50 can be usedto provide selectivity in an over-etch situation. During etching, theetchant gases are used to selectively etch away, for example,polysilicon which has been deposited on an oxide layer. Photoresistprotects the polysilicon which is not to be etched, while exposing thepolysilicon which is to be etched away. After etching away thepolysilicon, the underlying oxide layer is left. In some situations,small deposits of polysilicon remain in unwanted areas on top of theoxide substrate. Over-etching can be used to remove this unwantedpolysiiicon. However, over-etching can also undesirably etch into andremove the oxide layer. Through the use of the solid source, gas speciestherefrom can be used to ensure that the oxide substrate is not etched,while the remaining residual deposits of polysilicon are etched away. Inthis process, the species from the silicon dioxide source are depositedon both on the oxide substrate and on the residual polysilicon. However,the removal or etching rate of the polysilicon is higher than thedeposit rate of the species from the solid source onto the polysiliconand thus the residual polysilicon is etched away without damage to theoxide substrate.

During the above over-etch process, the plasma power supply 30 is turneddown and the DC bias 34 is lowered. By way of example only, the powersupply 30 is turned down to one watt and the DC power supply is turnedoff. The activation energy curve for an oxide versus a polysilicon issuch that as the energy is reduced, the polysilicon continues to beetched but at a slower rate while the etching of the oxide is reduced tonear zero.

In another example, a semiconductor wafer includes tungsten silicide(WSi₂) which have been deposited on a polysilicon layer, whichpolysilicon layer has been deposited on an oxide substrate. Anappropriate photoresist layer is placed on the wafer and the wafer isexposed to process gases in the etchant chamber 22. A first reaction gasetches away the tungsten silicide and sometimes leaves deposits oftungsten silicide, called stringers, especially in areas where thetungsten silicide and polysilicon have step features. It is in the baseof such steps that such stringers of tungsten silicide can be left. Byusing a solid source 50 as described above, the selectivity of the etchprocess can be controlled to preserve the underlying layers ofpolysilicon and oxide so that the physical dimensions and electricalperformance of the semiconductor device does not change in anyundesirable manner. Thus, using this method and controlling theselectivity, there is little or no attack of the underlying surface. Itis found that with the above arrangement, that the selectivity for theremoval of tungsten silicide to polysilicon is approximately 4 to 1. Inother words, the tungsten silicide is removed at a rate of approximatelyfour times greater than that of the polysilicon. Without such anarrangement, it is found that the selectivity is approximately 0.7 to 1,meaning that the tungsten silicide is etched at approximately 0.7 timesthe rate of etching of the polysilicon. Similar results are obtained forother types of metal silicides such as for example titanium suicides,cobalt silicides, and molybdenum silicides. It is these types of metalsuicides that are used for fabricating MOSFETs, LEDs, and flat paneldisplays.

Gaseous Source:

In addition to the above benefits described with respect to the gaseousspecies eroded from the solid source, such benefits can also be acquiredby introducing in the process gases, gases which have the effect derivedfrom the gaseous species eroded from the surface of the solid source. Byway of example only, a gaseous form of tetraethoxysilane (TEOS) can beintroduced with the process gas. TEOS is a source of silicon and oxygenfor the etching process. TEOS in the process chamber provides the samegaseous species as does a solid source of silicon dioxide (SiO₂) withthe advantages to the etching process described herein. Also it is to benoted that a combination of both solid source and a gaseous source ofsuch species would be within the spirit and scope of the invention.

Nozzles:

FIGS. 3a, 3 b, 4 a, 4 b, 4 c, 4 d, 5 a, 5 b, 5 c, 6 a, 6 b, and 6 cdepict alternative preferred embodiments of nozzle arrangements whichcan be used with the above invention. Conventional nozzle arrangementsare generally configured in a “shower head” configuration with as manyas 200 ports from which process gases to be ejected. The intent of suchan arrangement was to ensure that there was a uniform distribution ofthe process gases in the chamber, and in particular, at the surface ofthe semiconductor wafer that was being processed. Prior art devices havebeen found to create a layer of stagnate, used gases which have alreadyreacted with the wafer surface and thus dilute the uniformity of newprocess gases directed toward the surface. The present inventionimproves upon such prior art nozzles. The present invention includesnozzles which generate discrete collimated jets of process gases whichmerged together adjacent the wafer surface to create a uniformdistribution at the surface of the wafer. The velocity of the gases andthe volume in the jets assure that fresh process gas reaches the surfaceof the semiconductor wafer. Thus, fresh process gases are uniformallydistributed at the surface of the semiconductor wafer. These process gasjets stir up the gases at the surface of the wafer making a uniformdistribution of process gas and gaseous species eroded from the surfaceof the solid source.

FIGS. 3a and 3 b depict a one-port nozzle 90 with the port identified as92. The nozzle is preferably comprised of alumina. With thisarrangement, a single jet of gas is projected toward the semiconductorwafer.

FIGS. 4a, 4 b, 4 c, and 4 d depict another preferred embodiment of anozzle 94 of the invention which is also comprised of alumina. In thisembodiment, the nozzle 94 includes twelve ports which define jets ofprocess gas that are directed toward the semiconductor wafer.Preferably, the jets are directed at an angle which is skew to verticaland the centerline of each jet is directed toward the peripheral edge ofthe wafer. This arrangement is again beneficial in ensuring that thereis a uniform distribution of new process gases at the surface of thewafer. As can be seen in FIG. 4d, the ports are distributed around theperiphery of the face of the nozzle.

FIGS. 5a, 5 b, and 5 c depict a further embodiment of a nozzle 98 of theinvention. In this arrangement, the ports 99 are depicted in a starformation with some of the ports being provided on the periphery of theface (FIG. 5c) of the nozzle 98 while other of the ports are centrallylocated with one port on the centerline of the nozzle. As with the gasesfrom the nozzle of FIG. 4a, the jets of the nozzle of FIG. 5a are angledwith respect to the vertical and thus are directed both at the body ofthe semiconductor wafer and at the edge of the semiconductor wafer inorder to provide a uniform distribution of process gas.

FIGS. 6a, 6 b, and 6 c depict yet another preferred embodiment of thenozzle 100 of the invention. In this embodiment, ports 102 are directedessentially normal to a vertical line between the nozzle and thesemiconductor wafer. In this embodiment, the nozzles are directed towardthe solid source on the side wall in order to ensure greater mixing ofthe gas species from the solid source and the process gas.

Magnetic Confinement:

The above identified magnets 46, 47 provide a magnetic confinementaround reactor chamber 22 which ensures that a high density plasma canbe formed at low pressure. It is to be remembered that the plasma iscreated through a collision of gas atoms and electrons, generating ionsto create a high density plasma at low pressure. The present inventionachieves this by increasing the total path length of the electronstraveling through the plasma while minimizing ion loss to the reactorwall. The electrons traveling toward the plasma are reflected by themagnetic field back into the plasma thus increasing the path length ofthe electrons.

With the present invention, the magnets can either be electromagnets orpermanent magnets and be within the spirit and scope of the invention.These magnets, surrounding the etch chamber, create a magnetic fieldcontainer. The magnetic field effect exists only near the reactor walls,is virtually non-existent at the wafer, and creates an inherentlyuniform plasma. The magnets can provide the function of protecting theelectrodes as with a stronger magnetic confinement, there is lesserosion on the electrodes. A weaker confinement provides for moreerosion of the electrode and the solid source.

The magnetic confinement caused by the magnets 46, 47, thus is designedto concentrate the plasma and can have the effect of protecting theprocess chamber parts, including the electrodes from the corrosiveplasma. As a result, there can be considerable cost savings, as the costfor replacing the electrodes is reduced.

FIGS. 7 and 8 depict an arrangement of the magnet 46, 47, in associationwith the side electrode 26 and the upper electrode 24 respectively. Ascan be seen in FIG. 7 there are a plurality of slots 60 found relativeto the electrode 26. In a preferred embodiment, all of the slots arefilled with the magnet 46. For this particular embodiment, it isspecified that there are thirty-six ceramic magnets in electrode 26.These magnets each have a strength of about 300 Gauss to about 600 Gaussat the surface of the pole face. These magnets located behind the solidsource 50 affect the rate of erosion of gas species from the solidsource. As indicated above, without the magnets, it is possible that toomany gaseous species can be eroded from the solid surface and thusaffect the etch process.

It is to be noted that these magnets are pole face magnets. The northand south poles are on the faces 62 and the opposing faces 64 of themagnets. The magnets are arranged alternatively so that first a northpole face of one magnet 46 and then a south pole face of a second magnet46 are directed toward the center of the chamber. This is repeated aboutthe outer periphery of the electrode 26.

FIG. 8 depicts the arrangement of the magnets 47 associated with theupper electrode 24. In FIG. 8, all of the slot 66 are filled withmagnets similar to magnets 46. As in this particular embodiment, therewould be 36 magnets spoked out from the center of the electrode 24 sothat 36 magnet ends appear at the peripheral edge of the electrode 24.Again, these magnets are pole faced magnets, with the north and southpoles projecting from the side faces of the magnets. For theconfiguration of FIG. 8, the magnets alternate with the north and thenthe south poles facing towards the chamber.

It is to be understood that the above magnets can be replaced withstronger magnets such as rare earth magnets. In such situations, thenumber of magnets required would reduce in order to obtain comparablemagnetic confinements. The rare earth magnets could have a strength ofabout 1,500 Gauss to about 2,500 Gauss at the surface of the pole faceof the magnet. Preferably, the magnets would have the strength of about2,000 Gauss to about 2,200 Gauss at the surface of the magnet pole face.

Reactor Chamber:

The reactor chamber in the present invention has been specificallydesigned, as discussed above and below, in order to enhance theuniformity of the plasma. With respect to the physical characteristicsof the reactor chamber 22, as noted above, both the placement of thebaffle 40 and the nozzle 36, 70 contribute to the uniformity of theprocess gases in the reactor chamber 22. The baffle 40 ensures that thegas species eroded from the surface of the solid source 50 are notimmediately drawn up by the pump through the exhaust shaft 38, but areallowed to mix with the gases in the reactor chamber adjacent to thesemiconductor wafer 48. Additionally, the nozzle 38 having ports whichchannel jets of gases vertically, horizontally, and at skewed anglesensure that any gas species from the solid source are thoroughly mixedwith the process gases from the nozzle and that this uniform mixture isprovided to the semiconductor wafer 48.

The height of the reactor chamber from the nozzle to the surface of thesemiconductor wafer can be optimized. Prior art devices have a height of5¼″. It has been found that with the above described height and also thenozzle arrangements can be optimized in order to have the gas jets fromthe nozzle provide a uniform distribution of process gas at the surfaceof the semiconductor wafer. Thus, also for varying reactor heights,nozzle pattern compared to chamber pressure can be optimized for theetch process including the etch process using a solid source. Thisheight is irrespective of the diameter of the reactor chamber, althoughin a preferred embodiment, the reactor chamber is approximately 14½″ indiameter. By way of example only, for preferred operation at two tothree millitorr of pressure in the reactor chamber 22, the height of thereactor chamber would be preferably about 4″. For a height of less than4″, the jets would still be collimated and thus not uniformally spreadat the surface of the wafer. For a height greater than 4″, the jetscould merge together above the surface of the semiconductor wafer so asnot to provide a uniform distribution of process gases at the surface ofthe wafer.

Optimally, for a given nozzle configuration, it has been found that theproduct of the height of the reactor chamber 22 with the pressure in thechamber, should be constant in order to provide for optimal performance.Thus, as indicated above, optimal performance can be achieved with aheight of 4″ and a pressure of two to three millitorr. The range ofvalues for pressure and height include a height range of {fraction(1/10)} of an inch corresponding to 100 millitorr to a height of 10″corresponding to one millitorr for optimal performance. That is to saythat as the pressure increases in the reactor chamber, that the heightof the reactor chamber can be less and that as the pressure decreases,the height would increase in order to provide for optimal mixing of (1)the gases eroded from the solid source, (2) injected process gases, and(3) reaction products from the wafer surface.

The effect of the above invention is to (1) increase the selectivity(i.e., for example protect the oxide substrate), (2) enhance the profilecontrol of the etch process, and (3) enhance the line width control(i.e., protecting the photoresist from the etching process so that thecorrect line width is transferred from the photoresist to the wafer).

Industrial Applicability

It is seen that the present invention provides for an etching systemwhich provides for (1) a controlled anisotropic profile (i.e., straight,vertical sidewalls), while (2) etching selectively to minimize damage tothe underlayer substrate such as the oxide or other wafer materials, andwhile (3) etching uniformally over a non-uniform area in order to removestringers and other residual deposits. The present system provides foretching in the submicron range of less than 0.5 microns and preferablyless than 0.25 microns.

Accordingly, the present invention meets the above objects by providinga greater range of plasma densities through the reactor chamber. Thisrange of plasma densities is affected by the above referenced solidsource of gaseous species, the reactor chamber configuration includingthe protruding baffle and reactor height, the nozzle configuration, andthe configuration of the magnetic field. The density can then becontrolled by adjusting the power supply to one or more of theelectrodes.

Other features, aspects and objects of the invention can be obtainedfrom a review of the figures and the claims.

It is to be understood that other embodiments of the invention can bedeveloped and fall within the spirit and scope of the invention andclaims.

We claim:
 1. A method for etching a wafer in a plasma etch reactorcomprising the steps of: providing a reactor chamber with a solid sourceof gaseous species, the reactor chamber having a peripheral electrodeadjacent the solid source of gaseous species; controlling the rate ofgeneration of the gaseous species from the solid source by pulsing thepower level provided to the peripheral electrode in the reactor chamber;and allowing the gaseous species to passivate a surface of the wafer inorder to provide for anisotropic plasma etch of the wafer, the degree ofpassivation depending upon the rate of generation of the gaseous speciesfrom the solid source.
 2. The method of claim 1 wherein: saidcontrolling step is accomplished by controlling the frequency of powerprovided to the peripheral electrode in the reactor chamber.
 3. Themethod of claim 1 including: maintaining the reactor chamber at aboutless than a pressure of about 150 millitorr.
 4. The method of claim 1wherein: said controlling step is further accomplished by the selectionof the material for the solid source which is mounted in the reactorchamber.
 5. The method of claim 1 including: providing a protrudingbaffle in the reactor chamber in order to control the path of theprocess gasses in the reactor chamber and the concentration gradients ofthe process gasses.
 6. The method of claim 1 including the step of:using a first power supply at a first frequency and a second powersupply at a second frequency to control the generation rate from thesolid source and the plasma density.
 7. The method of claim 6 includingthe steps of: operating the first power supply at a high frequency; andoperating the second power supply at a low frequency.
 8. The method ofclaim 6 including the steps of: operating the first power supply in therange of about 2 MHz to about 950 MHz; and operating the second powersupply in the range of about 10 KHz to about 1 MHz.
 9. The method ofclaim 1 comprising the step of: magnetically confining the plasma in thereactor chamber with pole face magnets.
 10. The method of claim 1comprising the step of: magnetically confining the plasma in the reactorchamber with ceramic magnets.
 11. The method of claim 1 including thestep of: magnetically confining the plasma in the reactor chamber.
 12. Amethod for etching a wafer in a plasma etch reactor comprising the stepsof: generating a plasma in a reactor with one or more plasma gases, thereactor having a side peripheral electrode; generating a gaseous speciesfrom a solid source of gaseous species adjacent the side peripheralelectrode in the reactor, the gaseous species being generated withoutfirst reacting with a second species, the gaseous species further beinggenerated at a rate that is controlled by a level of power applied tothe side peripheral electrode; controlling the rate of generation of gasspecies from the solid source by pulsing the power applied to the sideperipheral electrode; and using the gas species from the solid source topassivate side walls of features on a wafer in order to accomplishanisotropic etch of the wafer, the rate of passivation depending on therate of generation of gaseous species from the solid source.
 13. Themethod of claim 12 wherein: said controlling step is accomplished bycontrolling the frequency of power provided to the side peripheralelectrode in the reactor chamber.
 14. The method of claim 12 including:maintaining the reactor chamber at about less than a pressure of about150 millitorr.
 15. The method step of claim 12 wherein: said controllingstep is further accomplished by the selection of the material for thesolid source which is mounted in the reactor chamber.
 16. The method ofclaim 12 including: using a first power supply at a first frequency anda second power supply at a second frequency to control the generationrate from the solid source and the plasma density.
 17. The method ofclaim 16 including the steps of: operating the first power supply at ahigh frequency; and operating the second power supply at a lowfrequency.
 18. The method of claim 16 including the steps of: operatingthe first power supply in the range of about 2 MHz to about 950 MHz; andoperating the second power supply in the range of about 10 KHz to about1 MHz.
 19. The method of claim 12 including the step of: magneticallyconfining the plasma in the reactor chamber.